They are all similar and they provide hosting services, which is basically a home for your project on the internet.
It’s like having a DropBox or GoogleDrive but for git-based projects.
This allows other people to see your stuff, synchronize it, and contribute.
For the R user, best simple straightforward resource out there is Happy git with R
Github itself has a dedicated section for learning in the docs and in particular, the Hello World tutorial will get you creating a repo, managing a branch and merging a pull request.
source https://www.nobledesktop.com/learn/git/git-branches